1. Field of the Invention
The present invention relates to an electromagnet drive apparatus which drives a relay used for controlling the switching on or off of the supply of electrical power to loads in; e.g., an electromobile.
1. Related Art
In reference to FIGS. 8 through 17, the prior art will be described. FIG. 8 is a circuit diagram illustrating the configuration of an electromagnet drive apparatus in the conventional art. FIG. 9 is a timing chart of the electromagnet drive apparatus, wherein (A) represents an on state of a switch, (B) represents the state of a pulse signal, (C) represents the state of an electrical current flowing through a coil, and (D) represents the state of a contact. FIG. 10 is a timing chart of the electromagnet drive apparatus, wherein (A) represents the state of the switch which is switched to an off state from an on state during the course of an operation, (B) represents the state of the pulse signal, (C) represents the state of the electrical current flowing through the coil, and (D) represents the state of the contact. FIG. 11 is a circuit diagram illustrating the configuration of a conventional electromagnet drive apparatus. FIG. 12 is a timing chart of the electromagnet drive system, wherein (A) represents the state of the switch which is changed to an off state from an on state during the course of the operation, (B) represents the state of the pulse signal, (C) represents the state of a second transistor, (D) represents the state of the electrical current flowing through the coil, and (E) represents the state of the contact. FIG. 13 is a timing chart of the electromagnet drive apparatus, wherein (A) represents the state of the switch which changes to an off state from an on state and further changes to the on state again during the course of the operation, (B) represents the state of the pulse signal, (C) represents the state of the second transistor, (D) represents the state of the electrical current flowing through the coil, and (E) and (F) represent the states of the contact, FIG. 14 is a circuit diagram illustrating the configuration of an electromagnet drive apparatus in another conventional art relating to FIG. 8,
FIG. 15 is a timing chart of the electromagnet drive apparatus, wherein (A) represents an on state of a switch, (B) represents the state of an electrical current flowing through a coil, and (C) represents the state of a contact, FIG. 16 is a circuit diagram illustrating the configuration of an electromagnet drive apparatus in another conventional art relating to FIG. 11, FIG. 17 is a timing chart of the electromagnet drive apparatus, wherein (A) represents an on state of a switch, (B) represents the state of an electrical current flowing through a coil, and (C) represents the state of a contact.
Electromagnet drive apparatuses have already been used in electromobiles or industrial equipment, wherein a plunger for closing or opening a contact is driven by an electromagnet within a relay for controlling the switching on or off of the supply of electrical power to loads.
A first example of this type of conventional electromagnet drive apparatus is illustrated in FIG. 8. This electromagnet drive apparatus is provided for a relay in order to close or open its contact U. The electromagnet drive apparatus is comprised of a field-effect transistor A which is connected in series with a coil X of the electromagnet and serves as a switching element, a pulse signal generation circuit B which generates a pulse signal for use in driving and turning on the transistor A on a predetermined cycle, and a regenerative circuit D which consists of a diode C serving as an electrical power absorbing element and is connected in parallel with the coil X so as to permit the flow of a regenerated electrical current when the field-effect transistor A is in an off state. Specifically, a switch Z is provided between a power supply Y and the coil X.
Next, the operation of the above-described electromagnet drive apparatus will be described. As illustrated in FIG. 9A, while the switch Z is in an on state, a voltage is applied to the coil X from the power supply Y, permitting flow of an electrical current through the coil X. As a result, the coil X is excited. As illustrated in FIG. 9C, the electrical current flowing through the coil X is maintained substantially constant as a result of switching on/off or so-called chopping operations in which the transistor A is turned on when it is driven on a predetermined cycle by a pulse signal in FIG. 9B received from the pulse signal generation circuit B. If the transistor A is in an on state, an electrical current flows into the coil X, so that the coil X is excited. Then, as illustrated in FIG. 9D, the contact U is turned on or is held in an on state, an electrical current flows into a load W from the power supply V. When the transistor A is turned off, the electrical current flowing through the coil X is regenerated by flowing through the diode C using a counter electromotive force developed in the coil X as a supply source. Therefore, even while the transistor A is in an off state, the coil X is excited, thereby turning on the contact U or maintaining the contact U in an on state as illustrated in FIG. 9D. Resultingly, an electrical current flows to the load W from the power supply V.
In contrast, when the switch Z is turned off as at time T1 in FIG. 10A, the electrical current flowing through the coil X gradually decreases as illustrated in FIG. 10C. At the same time, the attraction of the electromagnet also decreases gradually. When the electrical current decreases to a value less than a predetermined value I1 as illustrated in FIG. 10C, the contact U is opened as at time T2 in FIG. 10D after a slight delay (for example, 10 msec from time T1), thereby interrupting flow of an electrical current to the load W from the power supply V.
As shown in FIG. 14 and 15 (A) to (C), another conventional electromagnetic drive apparatus will be described. In FIG. 14, components which have substantially the same features as those of the components in the conventional art as shown in FIG. 8 are the same numerals, except of omitting the pulse signal generation circuit.
The operation of the device in FIG. 14, when the voltage is applied to a coil X, a direct current flows without a regenerating. If the power supply Y turns off, a regenerated electrical current flows through the regenerative diode D. As shown in FIG. 15 (A) to (C), the time of period for turning off the contact U is in 10 msec from time T1.
A second example of the same type of conventional electromagnet drive apparatus is illustrated in FIG. 11. This electromagnet drive apparatus is provided for a relay in order to close or open a contact U of the relay. The electromagnet drive apparatus is comprised of a first field-effect transistor A connected in series with a coil X of an electromagnet; a pulse signal generation circuit B which generates a pulse signal for use in driving and turning on the transistor A on a predetermined cycle; a regenerative circuit D which includes a diode C connected in series with a second transistor E and a Zener diode F, both of which are connected in parallel with each other, and is connected in parallel with the coil X so as to permit the flow of a regenerated electrical current when the field-effect transistor A is in an off state; and a third transistor G which controls the switching on or off of the second transistor E. Specifically, a switch Z is provided between a power supply Y and the coil X.
Next, the operation of the above-described electromagnet drive apparatus will be described. Similar to the first conventional example, while the switch Z is in an on state, a voltage is applied to the coil X from the power supply Y, permitting flow of an electrical current through the coil X. As a result, the coil X is excited. As in the case of the first conventional example, the electrical current flowing through the coil X is maintained constant as a result of chopping operations. While the transistor A is in an off state, the electrical current flowing through the coil X is regenerated by flowing through the regenerative circuit D using the counter electromotive force developed in the coil X as a supply source. Therefore, while the switch Z is in an on state, the coil X is excited, thereby turning on the contact U. Resultingly, an electrical current flows to the load W from the power supply V.
When the switch Z is turned off as at time T3 in FIG. 12A, the operation of the pulse signal generation circuit B is stopped as illustrated in FIG. 12B, thereby turning the first transistor A off. Further, if the switch Z is turned off, the third transistor G is also turned off, which in turn turns off the second transistor E as illustrated in FIG. 12C. At this time, the energy stored in the coil X causes an electrical current to flow to the Zener diode F and the diode C which form the regenerative circuit D. The Zener diode F quickly consumes the energy that is stored in the coil X when the switch Z is turned off, and hence the electrical current flowing through the coil X by means of the counter electromotive force decreases immediately as illustrated in FIG. 12D. Therefore, when the switch Z is turned off, the electrical current flowing through the coil X decreases immediately, so that the contact U is turned off immediately as at time T4 in FIG. 12E. As a result, the flow of the electrical current to the load W from the power supply V is interrupted. The time interval between time T3 and time T4 (for example, 0.5 msec) is shorter than the time interval between time T1 and time T2 in the first conventional example. Therefore, the second conventional example is improved as compared to the first conventional example in terms of an opening speed.
As shown in FIG. 16 and 17 (A) to (C), another conventional electromagnetic drive apparatus will be described. In FIG. 16, components which have substantially the same features as those of the components in the conventional art as shown in FIG. 11 are the same numerals, except of omitting the pulse signal generation circuit.
The operation of the device in FIG. 16 when the voltage is applied to a coil X, a direct current flows without a regenerating. If the power supply Y turns off, a regenerated electrical current flows through the regenerative diode D and Zener diode F. As shown in FIG. 17 (A) to (C), the time of period for turning off the contact U is in 0.5 msec from time T1".
In the electromagnet drive apparatus of the previously-described first conventional example, the electrical current flowing through the coil X is regenerated by flowing through the diode C using the counter electromotive force developed in the coil X as a supply source when the switch Z is turned off. However, the electrical current does not decrease very immediately and therefore continues flowing through the coil X by way of the diode C for a while. Consequently, the electromagnet remains in an on state, which may results in the risk of delayed opening of the contact of the relay. More specifically, the electrical current flowing through the coil X decreases mildly, and the attraction of the electromagnet also decreases mildly. Therefore, the opening speed of the contact of the relay is slow, thereby resulting in low breaking capability. For the case of such a slow opening speed, even in the event that it is necessary to immediately open the contact for reasons of a short circuit occurred in the circuit of the load W, there is a risk of a dangerous condition because the contact is not opened for a while. More specifically, for example, in case an electromobile causes a car accident or there are accidents to industrial equipment, a dangerous condition will result from a short circuit unless a relay provided in a circuit of a motor which is a power source is opened immediately.
In the electromagnet drive apparatus of the second conventional example, the Zener diode F immediately consumes the energy stored in the coil X when the switch Z is turned off, and the electrical current that flows through the coil X by means of the counter electromotive force decreases immediately. Therefore, the electromagnet can be turned off immediately. In other words, the electrical current flowing through the coil X decreases immediately, and the attraction of the electromagnet also decreases immediately. Therefore, the opening speed of the contact of the relay is improved, thereby resulting in improved breaking capability.
However, in this electromagnet drive apparatus, a contact switch or a semiconductor switch is used as the switch Z for controlling the switching on or off of the application of a supply voltage. For the case of the contact switch, there is a risk of momentarily erroneous switching off of the switch due to physical shock. Further, for the case of the semiconductor switch, there is a risk of momentarily erroneous switching off of the switch due to external noise or to faulty operations induced by a signal used for actuating the switch. More specifically, in a case where such an electromagnet drive apparatus is used with an electromobile or the like, the contact may be momentarily opened by vibrations resulting from the driving of the electromobile if the switch Z is a contact switch. Further, even in the case where the switch Z is a semiconductor switch, the switch may be momentarily interrupted by external noise caused by variations in the external environment associated with the driving of the electromobile.
As described above, even if there is unintentional turning off of the switch Z, there is a risk of immediate and erroneous switching off of the electromagnet, thereby resulting in abnormal operations of the contact of the relay.
More specifically, as illustrated in FIGS. 13A to 13C, even in a case where the switch Z is turned off unintentionally at time T5 for some reasons, and where the switch Z is turned on again at time T7 (for example, after 1 msec from T5) immediately after the switch Z has been turned off, the electrical current flowing through the coil X decreases immediately as illustrated in FIG. 13D. As illustrated in FIG. 13E, the contact U is opened at time T6 between time T5 and time T7 (for example, after 0.5 msec from T5).
In a case where the electrical current to maintain the contact U in an on state is set to a value larger than an electrical current required to close the contact U, if an electrical current which is larger than the predetermined value 11 and is necessary to turn the power on flows again as illustrated in FIG. 13E, the contact point U is turned on. In contrast, if an electrical current larger than the electrical current that maintains the contact point U in an on state is necessary to close the contact point U, the contact point U is not closed by the flow of the electrical current illustrated in FIG. 13D. As a result, the contact point U is continuously maintained in an off state after time T6 as illustrated in FIG. 13F.
The present invention has been conceived in terms of the foregoing drawbacks in the background art, and the object of the present invention is to provide an electromagnet drive apparatus which is capable of turning off an electromagnet immediately at a desired time and prevents the electromagnet from being erroneously turned off even if there is momentarily interruption of the supply of electrical power.
To solve the foregoing drawbacks, an electromagnet drive apparatus, according to the present invention, comprises: a switching element connected in series with a coil of an electromagnet; a pulse signal generation circuit which generates, on predetermined cycles, a pulse signal used for turning on the switching element; a diode connected in series with a parallel circuit which includes a switch section and a power absorbing element; a regenerative circuit which permits flow of a regenerated electrical current when the switch section is turned on and the switching element is turned off from a state in which the switch section and the switching element are in an on state and a source voltage is applied to the coil of the electromagnet, and which causes the power absorbing element to immediately reduce the regenerated electrical current flowing through the coil of the electromagnet when the switch section and the switching element are turned off; and a delay circuit which turns on the switch section by application of the supply voltage and maintains the switch section in an on state until a predetermined period of time elapses after the application of the supply voltage has been stopped.
An electromagnet drive apparatus, according to the present invention, comprises: the switch section including a transistor connected in parallel with the power absorbing element; a phototransistor connected between a base and a collector of the transistor; and a light-emitting diode which emits light so as to control the switching on or off of the phototransistor.
An electromagnet drive apparatus, according to the present invention, comprises: a switching element connected in series with a coil of an electromagnet; a pulse signal generation circuit which generates, on predetermined cycles, a pulse signal used for turning on the switching element; a regenerative circuit which includes a diode connected in series with a parallel circuit comprised of a switch section and a power absorbing element and is connected in parallel with a coil such that a regenerated electrical current flows when the switching element is in an off state; a phototransistor connected between a base and a collector of the transistor to control the switching on or off of the transistor; a light-emitting diode which emits light so as to control the switching on or off of the phototransistor; and a delay circuit which continues feeding an electrical current to the light-emitting diode until a predetermined period of time elapses after the application of the power has been stopped.
An electromagnet drive apparatus, according to the present invention, comprises: the delay circuit including: a capacitor which is capable of being charged during the application of the supply voltage and discharging an electrical current to the switch section until a predetermined period of time elapses after the application of the supply voltage has been stopped; and a Zener diode connected in parallel with the capacitor.
An electromagnet drive apparatus, according to the present invention, comprises: the delay circuit including a capacitor which is capable of being charged during the application of the supply voltage and discharging an electrical current to the switch section until a predetermined period of time elapses after the application of the supply voltage has been stopped; and the electromagnet drive apparatus being characterized by further comprising: a supply voltage detection circuit which applies a given charging voltage to the capacitor if the supply voltage is higher than a predetermined voltage but does not apply a voltage to the capacitor if the supply voltage is lower than a predetermined voltage.
An electromagnet drive apparatus, according to the present invention, comprises: a reference voltage circuit which outputs a reference voltages and a comparator which compares the reference voltage with the voltage across the capacitor and outputs a control signal for controlling the switching on or off of the switch section.